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         * 语法： 参数 => 表达式
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        // 示例1
        // function a(x){
        //     return x*2
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        // var a = function(x){
        //     return x*2
        // }

        // var a = x => x*2

        // console.log(a(6))

        // 示例2
        var b = (x,y) => x+y

        var c = () => 666

        var d = x => {
            x = x + 1
            console.log('hello')
            x = x*2
            return x
        }

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